1. Field of the Invention
The invention relates to a head-carrying mechanism for disk driving apparatus for double-side flexible disks, and more specifically to a support for a pair of heads which is utilized for reading and writing data on a flexible disk as is used in computers or word processors.
2. Description of the Prior Art
Several types of head carrying mechanisms have been in use, and efforts have been made to realize a mechanism which allows the head to follow faithfully the surface of the flexible disk while it rotates.
A typical prior art will be described hereinafter with reference to the drawings.
In the Specification of U.S. Pat. No. 4,089,029, a head carrier for the 0-side of a flexible disk (hereinafter cited as media) as well as a head carrier for the side-1 of the media is described. The FIGS. 9 to 14 show an example of aforementioned prior art. FIGS. 9 and 10 show a head carrying mechanism for 1-side surface of the media and FIGS. 11, 12, one for 0-side surface of the media respectively. The head carrying mechanism for side-0 surface and that for side-1 surface has the same structure except for the location of the head core 121 and pressure loading arm 125. The side 1 head 102 is held by a cantilever gimbal spring 103. The side 0 head 122 is held by a similar gimbal spring 123. Both heads 102, 122 have at their rear face projections 104, 124, which abut on the spring 105, 125. The gimbal 103, the projection 104, and the spring 105 form an unseparable part. Similarly, the gimbal 123, projection 124, and the spring 125 form another part as seen in FIG. 13. the gimbal 103 for the side 1 face, and the gimbal 123 for the side 0 face, is fixed on the members 107 and 127 respectively, which are fixed to the bottom of the arms 106 and 126 on either side of the media 100. To provide magnetic recording or reading, the heads 102, 122 are moved into contact with the rotating media surfaces.
The head carrying mechanism of the prior art shown in FIG. 13 has cantilever gimbals 103, 123, which are very flexible, and are capable of following a slight wobbling motion, radial or circumferential distortion of the media. The head is also capable of smaller head load force, i.e. force of contact of the head to a media surface.
However the head of the prior art has the drawback that good recording contact of the head can be easily damaged due to the wobbling of the head in case of excessive distortion or warp of the media, or inaccuracy of positioning of the media. In other words, the cantilever gimbal springs 103, 123, which carry the heads 102, 122 form cantilevers with one of their ends fixed to the arms 106, 126.
Another drawback is that when the cantilever springs carrying the heads 102, 122 are bent, and the heads 102, 122 are inclined to the media surfaces, the head cores 101, 121 are slightly radially displaced thereby causing hazardous effect on tracking accuracy.
The head carrying mechanism of the prior art has another drawback that complicates shape of the cantilever springs 103, 123 and require loading springs to have severe dimensional tolerances. The gimbal springs 103, 123 when they are removed from the assembly, show a spring back as shown in broken lines in FIGS. 9, 11 to give a pre-load to the head carrier when it is assembled. This spring back of the gimbal spring causes difficulty in keeping the head in a correct position when it is assembled into a head carrying mechanism.
FIGS. 15-17 show another prior art as disclosed in U.S. Pat. No. 4,151,573. A carriage 201 is provided on the side 0 face of a media 200. The carriage is movable in the radial direction with respect to the media. On the carriage 201 is fixed a button-shaped head 202. The head is in contact with the side 0 surface of the media. On the side 1 surface of the media is disposed a head 205 which is movable with respect to the media. The head 205 is fixed on a cantilever gimbal 204, which is held on an arm 203. One end of the arm 203 is hinged to the stem of the carriage 201. The head 205 has at its back a projection 206 which receives a loading force of a pivot 207 fixed on the arm 203. A coil spring 208 is provided on the stem of the arm to urge the pivot downward, or to the button-shaped head 202. The button-shaped head 202 for side 0 surface has a flat contact surface with its periphery chamfered. The contact surface of the head 202 is placed slightly above the level of the media surface to penetrate the media.
The head carrying mechanism of the last mentioned prior art has found a wide use because the head of this type has many advantages e.g. simplicity in structure, high reliability of tracking notwithstanding wobblings of the media due to the fact that the head is fixed directly on the carriage and no displacement of the head occurs.
However in order to yield the media to assure a good recording contact between the head and media surface, a comparatively high loading pressure is required, in particular when the media has undulations. To prevent excessive wear of the media, allowable loading pressure is limited. When the media has excessive undulations, a slight gap may occur between the head and the media surface, even if the greatest allowable loading pressure is applied on the head. Furthermore, when the accuracy of the position of the head with respect to the media surface is not sufficient, a gap can easily occur between the side 0 surface and the head which moves to the side 0 surface of the media because the tolerance in height of the head over the media surface is very tight. If the gap exceeds 0.2-0.3 .mu.m for a media having an ordinary recording density, recording or reading of data is impossible. The gap must be tighter for higher recording density. For this reason, this type of head carrying mechanism is not suitable for high density recording.
The head of this type has still other drawbacks that the side 1 head 205 receives a relatively great mass of the arm 203, and tends to damage the media when the head is moved to the media surface too rapidly, or contact pressure on the media surface is liable to change by the posture of the carriage.
FIGS. 18-20 show still another prior art as is shown in Japanese Utility Model Publication No. 61-34596 (U.S. Pat. No. 4,306,258). In the publication, a head is disposed on each side of the media. The head carrier of each side is similar in construction. The head is fixed on the center of the planar spring gimbal 302. The contact pressure is obtained by the spring back of the gimbal 302. The head carrying mechanism prevents dislocation of the head as long as no deformation occurs on the head carrying arm 303. The head carrying mechanism assures a good recording contact of the head due to the spring rate of the gimbal in the direction normal to the media face, and provides capability to the head of swing movement about the axis both circumferentially and radially with respect to the media.
However, the head carrying mechanism allows a radial dislocation of the head core gap as a result of swing motion about an axis parallel to the direction of the motion of the media. The dislocation of the head core gap occurs because the head slider, which is more than 2 mm in height, is tilted about the gimbal. The height of the head slider must be at least 2 mm to allow movement within the jacket of the media. The above-mentioned radial wobbling of the head core causes a dislocation of the head, i.e. off-tracking. As a result, severe allowance is posed on the track margin and this allowance is especially severe when a high density recording is employed in which a number of tracks per inch or per mm is very large. In a disk driving apparatus for a high density recording disk in which a servo tracking technology is employed, follow up control of too rapid off-tracking, i.e. high frequency of off-tracking, is impossible.
FIGS. 21-22 show the fourth example of prior art as shown in Japanese Patent Publication No. 58-43828, in which the heads 401, 402 are fixed at the center of gimbals 403, 404. One of the gimbals 404 is supported by radially spaced members at 404, 405.
The heads 401, 402 are supported on a carriage which is pivotable about an axis parallel to a radius of the media so that good circumferential follow-up of the heads can be achieved. In other words, the head is allowed to rock about a radial axis with respect to the media (pitching).
This type of head carrying mechanism allows for only a swing motion of the heads around an axis parallel to a radius of the media, and no swing motion around an axis parallel to the circumferential to the media nor wobbling to the direction normal to the media, is allowed. This means a gap can occur, when the relative height changes, between the head core and the media. When the supports 405, 406 are fixed on a carriage 407 with resilient members therebetween, the head is allowed to rock in the Z-X plane (rolling), which is undesirable.
FIG. 22 shows another type of gimbal which realizes similar functions as that shown in FIG. 21. The gimbal has a pair of bridges 411, 412, which allow the head to pitch. However, the gimbal does not allow the head to roll nor to move normal to the media face.